In this kind of air bag device for a front passenger seat, an air bag and an inflator are mounted to a retainer case such as a container. Also, a modular cover is mounted to the case so as to cover the bag. In case of an accident, the inflator operates to cause the air bag to inflate. Then, the modular cover is pushed by the inflating air bag and begins to open on the side of the passenger compartment. The air bag inflates greatly toward the passenger compartment to protect the passenger.
This modular cover is provided with a tear start line or bend start line. When the inflator operates, the modular cover is pushed by the air bag and tears or bends along the start line. Then, the cover begins to open on the side of the car interior.
When the air bag of the air bag device for a front passenger seat is expanded on a plane, each longer side portion swells outwardly in an arc. Therefore, when the air bag is folded away, the swelling longer side portions are not neatly folded away. This creates wasteful space inside the case, or it is difficult to insert the bag into the case.